Interesting. I think there's also other factors possibly at play here, such as learned behavior during masturbation, range of variety of physical structures, etc. For example, you might be an outlier in that you have a large penis, but maybe more nerve endings than most men with large penises and therefore, ejaculate faster naturally. Or it could be affected by learned behavior.
For myself, my learned behavior in masturbation was to make it last as long as possible. In addition, I have sometimes had trouble with physically achieving orgasm, even though I'm aroused and want it. It's frustrating to be sure, and has led to this as one possible reason, as I'm quite large, and I'd heard that other very large men had the same issue. But without a scientific study on this in particular, I don't know for sure, of course.